1. Field of the Invention
The present invention relates to a control system and control method for controlling operation of a torque converter lock-up clutch. In particular, the present invention relates to a control for controlling the torque converter lock-up clutch of an automated vehicular transmission system of the type including an internal combustion engine, a change-gear transmission, a fluid torque converter drivingly interposed between the engine and the transmission, a torque converter lock-up clutch and a control unit.
More particularly, the present invention relates to a control system/method for an automated transmission system of the type described above wherein the torque converter lock-up clutch is adaptively controlled as a function of sensed torque converter slip, transmission input shaft acceleration and/or time since the last change in lock-up status.
2. Description of the Prior Art
Automatic mechanical transmission systems comprising mechanical transmissions and controls and actuators to automatically shift same, usually electronically controlled in accordance with sensed inputs and predetermined logic rules, are known. Examples of such systems may be seen by reference to U.S. Pat. Nos. 4,648,290; 4,595,986; 4,527,447; 4,711,141; 4,792,901; 4,361,060; 5,089,956; 5,157,607; 4,140,031 and 4,081,065, the disclosures of which are incorporated herein by reference.
Fully or partially automated vehicular transmission systems utilizing a fluid torque converter drivingly interposed the engine and the multiple-speed transmission and including a torque converter lock-up and/or bypass clutch also are well known in the prior art. As is well known, at or above certain vehicle speeds, the torque multiplication and damping properties of torque converters are typically not necessary, and it is desirable to lock up the torque converter to minimize the fluid coupling power loss inherent in torque converters. Examples of such automated vehicular transmission systems may be seen by reference to U.S. Pat. Nos. 3,593,596; 4,252,223; 4,271,724; 4,375,171; 4,784,019; 4,860,861; 5,109,729 and 5,274,553, the disclosures of which are incorporated herein by reference. Examples of such systems also may be seen by reference to SAE Paper No. 881830, entitled The Eaton CEEMAT (Converter-Enhanced Electronically-Managed Automatic Transmission), the disclosure of which is incorporated herein by reference.
While the prior art automated vehicular transmission systems equipped with torque converters and torque converter lock-up clutches are widely used and commercially successful, they are not totally satisfactory, especially for use in heavy duty vehicles such as MVMA Class 5 and larger trucks and buses, as the torque converter lock-up clutch locked up at a fixed first transmission input shaft speed and unlocked at a fixed second transmission input shaft speed, which resulted in a lock-up clutch control which was not robust enough for various engine-vehicle combinations, was not adaptive for sensed current vehicle operating conditions (such as load and/or vehicle acceleration/deceleration) and/or under certain conditions, tended to "hunt" (i.e., to undesirably, rapidly cycle between locked up and unlocked conditions).